Weighted prediction for video coding

ABSTRACT

A device for processing video data includes a memory configured to store video data and one or more processors implemented in circuitry. The one or more processors are configured to generate a first weighting factor for a first reference picture in a first picture list using a second weighting factor for a second reference picture in a second picture list. The one or more processors are further configured to generate prediction information for a current block of video data using the first weighting factor and the second weighting factor.

This application claims the benefit of U.S. Provisional PatentApplication 62/787,701, filed Jan. 2, 2019, the entire content of whichis hereby incorporated by reference.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), the High Efficiency Video Coding (HEVC) standard, ITU-TH.265/High Efficiency Video Coding (HEVC), and extensions of suchstandards. The video devices may transmit, receive, encode, decode,and/or store digital video information more efficiently by implementingsuch video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

In general, this disclosure describes techniques for deriving aweighting factor for weighted prediction. The example techniques may beapplied to any of the existing and developing video codecs, such as HEVC(High Efficiency Video Coding), VVC (Versatile Video Coding) or be acoding tool corresponding to any other video coding standard. Inweighted prediction for bi-directional prediction, a video coder (e.g.,a video encoder or video decoder) may use a first weighting factor and asecond weighting factor to generate prediction information for a currentblock. In one or more examples described herein, the video coder may beconfigured to generate (e.g., derive, calculate, etc.) a first weightingfactor using the second weighting factor. In this way, the video encodermay refrain from signaling the first weighting factor in a bitstream,which may improve bandwidth efficiency because both weighting factors donot have be signaled.

In one example, a method of processing video includes generating, by oneor more processors implemented in circuitry, a first weighting factorfor a first reference picture in a first picture list using a secondweighting factor for a second reference picture in a second picturelist; and generating, by the one or more processors, predictioninformation for a current block of the video data using the firstweighting factor and the second weighting factor.

In another example, a device for processing video data includes a memoryconfigured to store video data and one or more processors implemented incircuitry. The one or more processors are configured to generate a firstweighting factor for a first reference picture in a first picture listusing a second weighting factor for a second reference picture in asecond picture list and generate prediction information for a currentblock of the video data using the first weighting factor and the secondweighting factor.

In one example, a computer-readable storage medium has stored thereoninstructions that, when executed, cause a processor to generate a firstweighting factor for a first reference picture in a first picture listusing a second weighting factor for a second reference picture in asecond picture list and generate prediction information for a currentblock of the video data using the first weighting factor and the secondweighting factor.

In another example, a device for coding video data includes means forgenerating a first weighting factor for a first reference picture in afirst picture list using a second weighting factor for a secondreference picture in a second picture list and means for generatingprediction information for a current block of the video data using thefirst weighting factor and the second weighting factor.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure, and a corresponding coding tree unit(CTU).

FIG. 3A is a conceptual diagram illustrating example spatial neighboringmotion vector (MV) candidates for merge mode.

FIG. 3B is a conceptual diagram illustrating example spatial neighboringMV candidates for advanced motion vector prediction (AMVP) mode.

FIG. 4A is a conceptual diagram illustrating an example temporal motionvector predictor (TMVP) candidate.

FIG. 4B is a conceptual diagram illustrating example motion vectorscaling.

FIG. 5A is a conceptual diagram illustrating example neighboring samplesof a current coding unit (CU) used for deriving illuminationcompensation (IC) parameters.

FIG. 5B is a conceptual diagram illustrating example neighboring samplesof a reference block used for deriving IC parameters.

FIG. 6 is a block diagram illustrating an example video encoder that mayperform the techniques of this disclosure.

FIG. 7 is a block diagram illustrating an example video decoder that mayperform the techniques of this disclosure.

FIG. 8 is a flowchart illustrating an example encoding process.

FIG. 9 is a flowchart illustrating an example decoding process.

FIG. 10 is a flowchart illustrating an example process for weightprediction.

DETAILED DESCRIPTION

As described in more detail below, the disclosure describes exampletechniques for using weighted prediction. Such techniques for weightedprediction may be applied to bi-directional prediction and otherprediction techniques. In an example of bi-directional prediction, avideo coder (e.g., a video encoder or a video decoder) may use a firstreference picture in a first picture list (e.g., list 0 or simply “L0”)and a second reference picture in a second picture list (e.g., list 1 orsimply “L1”) to generate prediction information for a current block ofvideo data. Rather than applying equal weightings to predictors from L0(e.g., a first block from a first reference picture from L0) andpredictors from L1 (e.g., a second block from a second reference picturefrom L1), the video coder may apply a first weighting factor topredictors from L0 and apply a second weighting factor to predictorsfrom L1. Using the first weighting factor and the second weightingfactor may improve an accuracy of a predicted block compared to systemsthat omit the first weighting factor and the second weighting factor(i.e., set the first weighting factor and the second weighting factor toone) and compared to systems that use only one weighting factor (e.g.,the first weighting factor and the second weighting factor is the same).

In some systems, a video encoder may signal the first weighting factorand the second weighting factor in a bitstream that includes video data.For instance, the video encoder may generate a bitstream that explicitlysignals the first weighting factor and the second weighting factor for acurrent block and a residual block for the current block. In thisexample, the video decoder may generate a predicted block using thefirst weighting factor and the second weighting factor for the currentblock. The video decoder may combine the predicted block with theresidual block to generate the current block.

Rather than signaling both the first weighting factor and the secondweighting factor for a current block, a video coder (e.g., video encoderor video decoder) may be configured to generate a first weighting factorfor a first reference picture in a first picture list using a secondweighting factor for a second reference picture in a second picturelist. For example, the video encoder may signal the second weightingfactor in a bitstream that includes video data and refrain fromsignaling the first weighting factor. In this example, the video decodermay generate the first weighting factor based on the second weightingfactor. For instance, the video decoder (and the video encoder) maygenerate the first weighting factor by calculating one minus the secondweighting factor, but other techniques (e.g., other than one minussecond weighting factor) to generate the first weighting factor based onthe second weighting factor are possible. In this way, the video codermay be configured to improve bandwidth efficiency of the video encoderand the video decoder compared to systems that explicitly signal boththe first weighting factor and the second weighting factor.

Techniques described herein for weighted prediction may be applied toany of the existing video codecs, such as HEVC (High Efficiency VideoCoding), VVC (Versatile Video Coding) or be an efficient coding tool inany future video coding standards. While examples of describestechniques related to weighted prediction are described with relation toHEVC and on-going works in Versatile Video Coding (VVC), techniquesdescribed herein may be applied to other existing video codecs and/orfuture video coding standards.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.The techniques of this disclosure are generally directed to coding(encoding and/or decoding) video data. In general, video data includesany data for processing a video. Thus, video data may include raw,uncoded video, encoded video, decoded (e.g., reconstructed) video, andvideo metadata, such as signaling data.

As shown in FIG. 1, system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may comprise any of awide range of devices, including a computer (e.g., a desktop computer, anotebook (e.g., laptop) computers, tablet computers, etc.), a set-topbox, a mobile device, (e.g., smartphone), a television, a camera, adisplay device, a digital media player, a video gaming console, a videostreaming device (e.g., a broadcast receiver device), or other devices.In some cases, source device 102 and destination device 116 may beequipped for wireless communication, and thus may be referred to aswireless communication devices.

In the example of FIG. 1, source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply the techniques for generating afirst weighting factor for a first reference picture in a first picturelist using a second weighting factor for a second reference picture in asecond picture list. Thus, source device 102 represents an example of avideo encoding device, while destination device 116 represents anexample of a video decoding device. In other examples, a source deviceand a destination device may include other components or arrangements.For example, source device 102 may receive video data from an externalvideo source, such as an external camera. Likewise, destination device116 may interface with an external display device, rather than includingan integrated display device.

In accordance with the techniques of this disclosure, a video coder(video encoder 200 or video decoder 300) may be configured to generate afirst weighting factor for a first reference picture in a first picturelist using a second weighting factor for a second reference picture in asecond picture list and generate prediction information for a currentblock of the video data using the first weighting factor and the secondweighting factor.

System 100 as shown in FIG. 1 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniques forgenerating a first weighting factor for a first reference picture in afirst picture list using a second weighting factor for a secondreference picture in a second picture list. Source device 102 anddestination device 116 are merely examples of such coding devices inwhich source device 102 generates coded video data for transmission todestination device 116. This disclosure refers to a “coding” device as adevice that performs coding (encoding and/or decoding) of data. Thus,video encoder 200 and video decoder 300 represent examples of codingdevices, in particular, a video encoder and a video decoder,respectively. In some examples, source device 102 and/or destinationdevice 116 may operate in a substantially symmetrical manner such thateach of source device 102 and/or destination device 116 include videoencoding and decoding components. Hence, system 100 may support one-wayor two-way video transmission between source device 102 and destinationdevice 116, e.g., for video streaming, video playback, videobroadcasting, or video telephony.

In general, video source 104 represents a source of video data (i.e.,raw, uncoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some example, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally, oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although shown separately from video encoder 200 and videodecoder 300 in this example, it should be understood that video encoder200 and video decoder 300 may also include internal memories forfunctionally similar or equivalent purposes. Furthermore, memories 106,120 may store encoded video data, e.g., output from video encoder 200and input to video decoder 300. In some examples, portions of memories106, 120 may be allocated as one or more video buffers, e.g., to storeraw, decoded, and/or encoded video data.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may modulate a transmission signalincluding the encoded video data, and input interface 122 may modulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 102 to destination device 116.

In some examples, source device 102 may output encoded data from outputinterface 108 to storage device 112. Similarly, destination device 116may access encoded data from storage device 112 via input interface 122.Storage device 112 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output encoded video data tofile server 114 or another intermediate storage device that may storethe encoded video generated by source device 102. Destination device 116may access stored video data from file server 114 via streaming ordownload. File server 114 may be any type of server device capable ofstoring encoded video data and transmitting that encoded video data tothe destination device 116. File server 114 may represent a web server(e.g., for a website), a File Transfer Protocol (FTP) server, a contentdelivery network device, or a network attached storage (NAS) device.Destination device 116 may access encoded video data from file server114 through any standard data connection, including an Internetconnection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on file server 114. File server 114 and input interface 122 maybe configured to operate according to a streaming transmission protocol,a download transmission protocol, or a combination thereof.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receiver, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 comprise wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 comprises a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 (e.g., storage device 112,file server 114, or the like). The encoded video bitstreamcomputer-readable medium 110 may include signaling information definedby video encoder 200, which is also used by video decoder 300, such assyntax elements having values that describe characteristics and/orprocessing of video blocks or other coded units (e.g., slices, pictures,groups of pictures, sequences, or the like). Display device 118 displaysdecoded pictures of the decoded video data to a user. Display device 118may represent any of a variety of display devices such as a cathode raytube (CRT), a liquid crystal display (LCD), a plasma display, an organiclight emitting diode (OLED) display, or another type of display device.

Although not shown in FIG. 1, in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may comprise an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

Video encoder 200 and video decoder 300 may operate according to a videocoding standard, such as ITU-T H.265, also referred to as HighEfficiency Video Coding (HEVC) or extensions thereto, such as themulti-view and/or scalable video coding extensions. Alternatively, videoencoder 200 and video decoder 300 may operate according to otherproprietary or industry standards, such as the Joint Exploration TestModel (JEM) or ITU-T H.266, also referred to as Versatile Video Coding(VVC). A recent draft of the VVC standard is described in Bross, et al.“Versatile Video Coding (Draft 7),” Joint Video Experts Team (JVET) ofITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 16^(th) Meeting: Geneva,CH, 1-11 Oct. 2019, JVET-P2001-v9 (hereinafter “VVC Draft 7”). Thetechniques of this disclosure, however, are not limited to anyparticular coding standard.

Examples of video coding standards may include, but is not limited to,ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 or ISO/IEC MPEG-2Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-T H.264 (also knownas ISO/IEC MPEG-4 AVC), including its Scalable Video Coding (SVC) andMulti-view Video Coding (MVC) extensions.

In addition, a new video coding standard, namely High Efficiency VideoCoding (HEVC) or ITU-T H.265, including its range extension, multiviewextension (MV-HEVC) and scalable extension (SHVC), has recently beendeveloped by the Joint Collaboration Team on Video Coding (JCT-VC) aswell as Joint Collaboration Team on 3D Video Coding ExtensionDevelopment (JCT-3V) of ITU-T Video Coding Experts Group (VCEG) andISO/IEC Motion Picture Experts Group (MPEG).

The latest HEVC draft specification, and referred to as HEVC WDhereinafter, is available fromhttp://phenix.int-evry.fr/jct/doc_end_user/documents/14_Vienna/wg11/JCTVC-N1003-v1.zip.

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) are now studyingthe potential need for standardization of future video coding technologywith a compression capability that significantly exceeds that of thecurrent HEVC standard (including its current extensions and near-termextensions for screen content coding and high-dynamic-range coding). Thegroups are working together on this exploration activity in a jointcollaboration effort known as the Joint Video Exploration Team (JVET) toevaluate compression technology designs proposed by their experts inthis area. The JVET first met during 19-21 Oct. 2015. The latest versionof reference software, i.e., Joint Exploration Model 7 (JEM 7) could bedownloaded from:https://jvet.hhi.fraunhofer.de/svn/svn_HMJEMSoftware/tags/HM-16.6-JEM-7.0/.Algorithm description of Joint Exploration Test Model 7 (JEM7) could bereferred to JVET-G1001.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data. In general, video encoder 200 and video decoder300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.That is, rather than coding red, green, and blue (RGB) data for samplesof a picture, video encoder 200 and video decoder 300 may code luminanceand chrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). According to HEVC, a video coder(such as video encoder 200) partitions a coding tree unit (CTU) into CUsaccording to a quadtree structure. That is, the video coder partitionsCTUs and CUs into four equal, non-overlapping squares, and each node ofthe quadtree has either zero or four child nodes. Nodes without childnodes may be referred to as “leaf nodes,” and CUs of such leaf nodes mayinclude one or more PUs and/or one or more TUs. The video coder mayfurther partition PUs and TUs. For example, in HEVC, a residual quadtree(RQT) represents partitioning of TUs. In HEVC, PUs representinter-prediction data, while TUs represent residual data. CUs that areintra-predicted include intra-prediction information, such as anintra-mode indication.

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to JEM. According to JEM, a video coder(such as video encoder 200) partitions a picture into a plurality ofcoding tree units (CTUs). Video encoder 200 may partition a CTUaccording to a tree structure, such as a quadtree-binary tree (QTBT)structure. The QTBT structure of JEM removes the concepts of multiplepartition types, such as the separation between CUs, PUs, and TUs ofHEVC. A QTBT structure of JEM includes two levels: a first levelpartitioned according to quadtree partitioning, and a second levelpartitioned according to binary tree partitioning. A root node of theQTBT structure corresponds to a CTU. Leaf nodes of the binary treescorrespond to coding units (CUs).

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT structure to represent each of the luminance and chrominancecomponents, while in other examples, video encoder 200 and video decoder300 may use two or more QTBT structures, such as one QTBT structure forthe luminance component and another QTBT structure for both chrominancecomponents (or two QTBT structures for respective chrominancecomponents).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning per HEVC, QTBT partitioning according to JEM, orother partitioning structures. For purposes of explanation, thedescription of the techniques of this disclosure is presented withrespect to QTBT partitioning. However, it should be understood that thetechniques of this disclosure may also be applied to video codersconfigured to use quadtree partitioning, or other types of partitioningas well.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU will have 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU generally has N samples in a vertical direction andN samples in a horizontal direction, where N represents a nonnegativeinteger value. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay comprise N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter-prediction or intra-prediction.Inter-prediction generally refers to predicting the CU from data of apreviously coded picture, whereas intra-prediction generally refers topredicting the CU from previously coded data of the same picture. Toperform inter-prediction, video encoder 200 may generate the predictionblock using one or more motion vectors. Video encoder 200 may generallyperform a motion search to identify a reference block that closelymatches the CU, e.g., in terms of differences between the CU and thereference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

VVC and JEM also provide an affine motion compensation mode, which maybe considered an inter-prediction mode. In affine motion compensationmode, video encoder 200 may determine two or more motion vectors thatrepresent non-translational motion, such as zoom in or out, rotation,perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select anintra-prediction mode to generate the prediction block. VVC and JEMprovide sixty-seven intra-prediction modes, including variousdirectional modes, as well as planar mode and DC mode. In general, videoencoder 200 selects an intra-prediction mode that describes neighboringsamples to a current block (e.g., a block of a CU) from which to predictsamples of the current block. Such samples may generally be above, aboveand to the left, or to the left of the current block in the same pictureas the current block, assuming video encoder 200 codes CTUs and CUs inraster scan order (left to right, top to bottom).

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter-prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directionalinter-prediction, for example, video encoder 200 may encode motionvectors using advanced motion vector prediction (AMVP) or merge mode.Video encoder 200 may use similar modes to encode motion vectors foraffine motion compensation mode.

Following prediction, such as intra-prediction or inter-prediction of ablock, video encoder 200 may calculate residual data for the block. Theresidual data, such as a residual block, represents sample by sampledifferences between the block and a prediction block for the block,formed using the corresponding prediction mode. Video encoder 200 mayapply one or more transforms to the residual block, to producetransformed data in a transform domain instead of the sample domain. Forexample, video encoder 200 may apply a discrete cosine transform (DCT),an integer transform, a wavelet transform, or a conceptually similartransform to residual video data. Additionally, video encoder 200 mayapply a secondary transform following the first transform, such as amode-dependent non-separable secondary transform (MDNSST), a signaldependent transform, a Karhunen-Loeve transform (KLT), or the like.Video encoder 200 produces transform coefficients following applicationof the one or more transforms.

As noted above, following any transforms to produce transformcoefficients, video encoder 200 may perform quantization of thetransform coefficients. Quantization generally refers to a process inwhich transform coefficients are quantized to possibly reduce the amountof data used to represent the coefficients, providing furthercompression. By performing the quantization process, video encoder 200may reduce the bit depth associated with some or all of thecoefficients. For example, video encoder 200 may round an n-bit valuedown to an m-bit value during quantization, where n is greater than m.In some examples, to perform quantization, video encoder 200 may performa bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) coefficients at the front of the vector and to place lowerenergy (and therefore higher frequency) transform coefficients at theback of the vector. In some examples, video encoder 200 may utilize apredefined scan order to scan the quantized transform coefficients toproduce a serialized vector, and then entropy encode the quantizedtransform coefficients of the vector. In other examples, video encoder200 may perform an adaptive scan. After scanning the quantized transformcoefficients to form the one-dimensional vector, video encoder 200 mayentropy encode the one-dimensional vector, e.g., according tocontext-adaptive binary arithmetic coding (CABAC). Video encoder 200 mayalso entropy encode values for syntax elements describing metadataassociated with the encoded video data for use by video decoder 300 indecoding the video data.

To perform CABAC, video encoder 200 may assign a context within acontext model to a symbol to be transmitted. The context may relate to,for example, whether neighboring values of the symbol are zero-valued ornot. The probability determination may be based on a context assigned tothe symbol.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,to video decoder 300, e.g., in a picture header, a block header, a sliceheader, or other syntax data, such as a sequence parameter set (SPS),picture parameter set (PPS), or video parameter set (VPS). Video decoder300 may likewise decode such syntax data to determine how to decodecorresponding video data.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information of apicture into CTUs, and partitioning of each CTU according to acorresponding partition structure, such as a QTBT structure, to defineCUs of the CTU. The syntax elements may further define prediction andresidual information for blocks (e.g., CUs) of video data.

The residual information may be represented by, for example, quantizedtransform coefficients. Video decoder 300 may inverse quantize andinverse transform the quantized transform coefficients of a block toreproduce a residual block for the block. Video decoder 300 uses asignaled prediction mode (intra- or inter-prediction) and relatedprediction information (e.g., motion information for inter-prediction)to form a prediction block for the block. Video decoder 300 may thencombine the prediction block and the residual block (on asample-by-sample basis) to reproduce the original block. Video decoder300 may perform additional processing, such as performing a deblockingprocess to reduce visual artifacts along boundaries of the block.

In accordance with the techniques of this disclosure, video encoder 200and/or video decoder 300 may be configured to generate a first weightingfactor for a first reference picture in a first picture list using asecond weighting factor for a second reference picture in a secondpicture list; and generate prediction information using the firstweighting factor and the second weighting factor and to generateprediction information using the first weighting factor and the secondweighting factor. Generating the first weighting factor may reduce anamount of data transmitted from video encoder 200 to video decoder 300compared to systems that explicitly signal the first weighting factor,which may reduce a power consumption of video encoder 200 and/or videodecoder 300 and/or improve a performance of video encoder 200 and/orvideo decoder 300 compared to systems that explicitly signal the firstweighting factor.

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values syntax elements and/or other data used to decodeencoded video data. That is, video encoder 200 may signal values forsyntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

FIGS. 2A and 2B are conceptual diagram illustrating an example quadtreebinary tree (QTBT) structure 130, and a corresponding coding tree unit(CTU) 132. The solid lines represent quadtree splitting, and dottedlines indicate binary tree splitting. In each split (i.e., non-leaf)node of the binary tree, one flag is signaled to indicate whichsplitting type (i.e., horizontal or vertical) is used, where 0 indicateshorizontal splitting and 1 indicates vertical splitting in this example.For the quadtree splitting, there is no need to indicate the splittingtype, since quadtree nodes split a block horizontally and verticallyinto 4 sub-blocks with equal size. Accordingly, video encoder 200 mayencode, and video decoder 300 may decode, syntax elements (such assplitting information) for a region tree level of QTBT structure 130(i.e., the solid lines) and syntax elements (such as splittinginformation) for a prediction tree level of QTBT structure 130 (i.e.,the dashed lines). Video encoder 200 may encode, and video decoder 300may decode, video data, such as prediction and transform data, for CUsrepresented by terminal leaf nodes of QTBT structure 130.

In general, CTU 132 of FIG. 2B may be associated with parametersdefining sizes of blocks corresponding to nodes of QTBT structure 130 atthe first and second levels. These parameters may include a CTU size(representing a size of CTU 132 in samples), a minimum quadtree size(MinQTSize, representing a minimum allowed quadtree leaf node size), amaximum binary tree size (MaxBTSize, representing a maximum allowedbinary tree root node size), a maximum binary tree depth (MaxBTDepth,representing a maximum allowed binary tree depth), and a minimum binarytree size (MinBTSize, representing the minimum allowed binary tree leafnode size).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. The example of QTBT structure 130 represents such nodes asincluding the parent node and child nodes having solid lines forbranches. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), they can be furtherpartitioned by respective binary trees. The binary tree splitting of onenode can be iterated until the nodes resulting from the split reach theminimum allowed binary tree leaf node size (MinBTSize) or the maximumallowed binary tree depth (MaxBTDepth). The example of QTBT structure130 represents such nodes as having dashed lines for branches. Thebinary tree leaf node is referred to as a coding unit (CU), which isused for prediction (e.g., intra-picture or inter-picture prediction)and transform, without any further partitioning. As discussed above, CUsmay also be referred to as “video blocks” or “blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If theleaf quadtree node is 128×128, it will not be further split by thebinary tree, since the size exceeds the MaxBTSize (i.e., 64×64, in thisexample). Otherwise, the leaf quadtree node will be further partitionedby the binary tree. Therefore, the quadtree leaf node is also the rootnode for the binary tree and has the binary tree depth as 0. When thebinary tree depth reaches MaxBTDepth (4, in this example), no furthersplitting is permitted. When the binary tree node has width equal toMinBTSize (4, in this example), it implies no further horizontalsplitting is permitted. Similarly, a binary tree node having a heightequal to MinBTSize implies no further vertical splitting is permittedfor that binary tree node. As noted above, leaf nodes of the binary treeare referred to as CUs and are further processed according to predictionand transform without further partitioning.

In HEVC, the largest coding unit in a slice is called a coding treeblock (CTB) or coding tree unit (CTU). A CTB contains a quad-tree thenodes of which are coding units. The size of a CTB can range from 16×16to 64×64 in the HEVC main profile (although technically 8×8 CTB sizescan be supported). A coding unit (CU) could be the same size of a CTB toas small as 8×8. Video encoder 200 and/or video decoder 300 may codeeach coding unit with one mode, i.e. inter or intra. When a CU is intercoded, video encoder 200 and/or video decoder 300 may further partitionthe CU into 2 or 4 prediction units (PUs) or become just one PU whenfurther partition does not apply. When two PUs are present in one CU,the two PUs can be half size rectangles or two rectangle size with ¼ or¾ size of the CU.

When the CU is inter coded, each PU has one set of motion information,which is derived with a unique inter prediction mode. In the HEVCstandard, there are two inter prediction modes, named merge (skip isconsidered as a special case of merge) and advanced motion vectorprediction (AMVP) modes respectively for a prediction unit (PU).

In either AMVP or merge mode, video encoder 200 and/or video decoder 300may maintain a motion vector (MV) candidate list for multiple motionvector predictors. Video encoder 200 and/or video decoder 300 may beconfigured to generate the motion vector(s), as well as referenceindices in the merge mode, of the current PU by taking one candidatefrom the MV candidate list.

The MV candidate list contains up to 5 candidates for the merge mode andonly two candidates for the AMVP mode. A merge candidate may contain aset of motion information, e.g., motion vectors corresponding to bothreference picture lists (list 0 and list 1) and the reference indices.If a merge candidate is identified by a merge index, video encoder 200and/or video decoder 300 may be configured to use the reference picturesfor the prediction of the current blocks, as well as the associatedmotion vectors are determined. Under AMVP mode for each potentialprediction direction from either list 0 or list 1, video encoder 200 maybe configured to explicitly signal a reference index needs, togetherwith an MV predictor (MVP) index to the MV candidate list because theAMVP candidate contains only a motion vector. In AMVP mode, videoencoder 200 and/or video decoder 300 may be configured to further refinethe predicted motion vectors. Video encoder 200 and/or video decoder 300may be configured to derive the candidates for both modes similarly fromthe same spatial and temporal neighboring blocks.

In accordance with the techniques of the disclosure, video encoder 200and/or video decoder 300 may generate a first picture list (e.g., list 0or simply “L0”) and a second picture list (e.g., list 1 or simply “L1”).For instance, video decoder 300 may decode information signaled in abitstream by video encoder 200 that indicates the first picture listand/or the second picture list. In some instances, video encoder 200and/or video decoder 300 may derive the first picture list and/or thesecond picture list based on implicit techniques.

Video encoder 200 and/or video decoder 300 may select a first referencepicture from the first picture list and/or a second reference picturefrom the second picture list. For example, video decoder 300 may decodeinformation signaled in a bitstream by video encoder 200 that indicatesan index of the first reference picture in the first picture list and/ora second reference picture from the second picture list. In someexamples, video encoder 200 and/or video decoder 300 may select thefirst reference picture in the first picture list and/or a secondreference picture from the second picture list based on implicittechniques.

Video encoder 200 and/or video decoder 300 may use the first referencepicture in the first picture list and/or a second reference picture fromthe second picture list to determine a first weighting factor for afirst reference picture. For example, video encoder 200 may determinethe second weighting factor that results in a predicted block thatminimizes a difference between a resulting predicted block and a currentblock. In this example, video encoder 200 may signal the secondweighting factor in a bitstream. For instance, video encoder 200 maysignal the second weighting factor within a symbol for a reference indexthat indicates (e.g., specifies) the second reference picture in thesecond picture list. More specifically, for example, video encoder 200may signal the second weighting factor within a symbol for a referenceindex using binarization according to selection probability as describedfurther herein, using truncated binary as described further herein, oranother technique. Video decoder 300 may decode the second weightingfactor and generate the first weighting factor for a first referencepicture in a first reference picture based on the second weightingfactor in accordance with techniques described herein. In some examples,video encoder 200 and/or video decoder 300 derive the first weightingfactor and the second weighting factor based on implicit techniques.

FIG. 3A is a conceptual diagram illustrating example spatial neighboringmotion vector candidates 340A-344A for merge mode. FIG. 3B is aconceptual diagram illustrating example spatial neighboring motionvector candidates for advanced motion vector prediction mode. Videoencoder 200 and/or video decoder 300 may be configured to derive spatialcandidates from the neighboring blocks shown in FIGS. 3A and 3B, for aspecific PU (PU₀), although the techniques for generating the candidatesfrom the blocks differ for merge and AMVP modes.

In the merge mode example shown in FIG. 3A, video encoder 200 and/orvideo decoder 300 may be configured to derive up to four spatial MVcandidates with the orders showed in FIG. 3A with numbers, and the orderis the following: left (0, A1), above (1, B1), above right (2, B0),below left (3, A0), and above left (4, B2). For example, video encoder200 or video decoder 300 may determine a first spatial MV candidateusing block 340A, a second spatial MV candidate using block 341A, athird spatial MV candidate using block 343A, and a fourth spatial MVcandidate using block 344A.

In the AVMP mode example shown in FIG. 3B, video encoder 200 and/orvideo decoder 300 may be configured to divide neighboring blocks intotwo groups: left group consisting of the block 340B and block 341B, andabove group consisting of block 342B, 343B, and 344B as shown in FIG.3B. For each group, the potential candidate in a neighboring blockreferring to the same reference picture as that indicated by thesignaled reference index has the highest priority to be chosen to form afinal candidate of the group. It is possible that all neighboring blocksdo not contain a motion vector pointing to the same reference picture.Therefore, if such a candidate cannot be found, video encoder 200 and/orvideo decoder 300 may be configured to scale the first availablecandidate to form the final candidate, thus the temporal distancedifferences can be compensated.

FIG. 4A is a conceptual diagram illustrating an example temporal motionvector predictor (TMVP) candidate. FIG. 4B is a conceptual diagramillustrating example motion vector scaling. Video encoder 200 and/orvideo decoder 300 may be configured to add a TMVP candidate, if enabledand available, into the MV candidate list after spatial motion vectorcandidates. The process of motion vector derivation for TMVP candidatemay be the same for both merge and AMVP modes, however the targetreference index for the TMVP candidate in the merge mode is always setto 0.

The primary block location for TMVP candidate derivation is the bottomright block outside of the collocated PU as shown in FIG. 4A as a block“T” 446, to compensate the bias to the above and left blocks used togenerate spatial neighboring candidates. However, if block T 446 islocated outside of the current CTB row or motion information is notavailable, video encoder 200 and/or video decoder 300 may be configuredto substitute the block with a center block 447 of the PU 448.

FIG. 4B is a conceptual diagram illustrating example motion vectorscaling. In the example of FIG. 4B, video encoder 200 and/or videodecoder 300 may be configured to derive a motion vector for TMVPcandidate from the co-located PU of the co-located picture 449,indicated in the slice level. The motion vector for the co-located PU iscalled collocated MV.

Similar to temporal direct mode in AVC, to derive the TMVP candidatemotion vector, video encoder 200 and/or video decoder 300 may beconfigured to scale the co-located MV to compensate the temporaldistance differences, as shown in FIG. 4B. Motion vector scaling isdiscussed in the following. The value of motion vectors may beproportional to the distance of pictures in the presentation time. Amotion vector may associate two pictures, the reference picture, and thepicture containing the motion vector (namely the containing picture).When video encoder 200 and/or video decoder 300 utilize a motion vectorto predict the other motion vector, video encoder 200 and/or videodecoder 300 may be configured to calculate the distance of thecontaining picture and the reference picture based on the Picture OrderCount (POC) values.

For a motion vector to be predicted, both containing picture associatedwith the motion vector and reference picture may be different.Therefore, video encoder 200 and/or video decoder 300 may be configuredto calculate a new distance (based on POC). In some examples, videoencoder 200 and/or video decoder 300 may be configured to scale themotion vector based on these two POC distances. For a spatialneighboring candidate, the containing pictures for the two motionvectors are the same, while the reference pictures are different. InHEVC, motion vector scaling applies to both TMVP and AMVP for spatialand temporal neighboring candidates.

Artificial motion vector candidate generation is discussed in thefollowing. If a motion vector candidate list is not complete, videoencoder 200 and/or video decoder 300 may be configured to generateartificial motion vector candidates and insert the artificial motionvector candidates at the end of the list until it will have allcandidates.

In merge mode, there are two types of artificial MV candidates: combinedcandidate derived only for B-slices and zero candidates used only forAMVP if the first type does not provide enough artificial candidates.For each pair of candidates that are already in the candidate list andhave necessary motion information, video encoder 200 and/or videodecoder 300 may be configured to derive bi-directional combined motionvector candidates by a combination of the motion vector of the firstcandidate referring to a picture in the list 0 and the motion vector ofa second candidate referring to a picture in the list 1.

Pruning process for candidate insertion is discussed in the following.Candidates from different blocks may happen to be the same, whichdecreases the efficiency of a merge/AMVP candidate list. Video encoder200 and/or video decoder 300 may be configured to apply a pruningprocess to solve this problem. The pruning process compares onecandidate against the others in the current candidate list to avoidinserting identical candidate in certain extent. To reduce thecomplexity, video encoder 200 and/or video decoder 300 may be configuredto apply only limited numbers of pruning process instead of comparingeach potential one with all the other existing ones.

In development of Versatile Video Coding (VVC), there are several intercoding tools which derive or refine the candidate list of motion vectorprediction or merge prediction for current block.

Zhang, et al. “CE4-related: History-based Motion Vector Prediction,”Joint Video Experts Team (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC29/WG 11, 11^(th) Meeting: Ljubljana, SI, 10-18 Jul. 2018, JVET-K0104-v5(hereinafter “JVET-K0104”) describes a History-based motion vectorprediction (HMVP) is a history-based process that allows each block tofind a respective block's MV predictor from a list of MVs decoded fromthe past in additional to those in immediately adjacent causalneighboring motion fields. Video encoder 200 and/or video decoder 300may be configured to maintain a table with multiple HMVP candidatesduring the encoding/decoding process. Video encoder 200 and/or videodecoder 300 may be configured to empty the table when a new slice isencountered. Whenever there is an inter-coded block, video encoder 200and/or video decoder 300 may be configured to insert the associatedmotion information to the table in a first-in-first-out (FIFO) fashionas a new HMVP candidate. Video encoder 200 and/or video decoder 300 maybe configured to a apply constraint FIFO rule. When inserting a HMVP tothe table, video encoder 200 and/or video decoder 300 may be configuredto apply a redundancy check to find whether there is an identical HMVPin the table. If found, video encoder 200 and/or video decoder 300 maybe configured to remove that particular HMVP from the table and move allthe HMVP candidates afterwards.

HMVP candidates could be used in the merge candidate list constructionprocess. Video encoder 200 and/or video decoder 300 may be configured toinsert all HMVP candidates from the last entry to the first entry in thetable after the TMVP candidate. Video encoder 200 and/or video decoder300 may be configured to apply pruning on the HMVP candidates. Once thetotal number of available merge candidates reaches the signaledmaximally allowed merge candidates, video encoder 200 and/or videodecoder 300 may be configured to terminate the merge candidate listconstruction process.

Similarly, video encoder 200 and/or video decoder 300 may be configuredto use HMVP candidates in the AMVP candidate list construction process.For example, video encoder 200 and/or video decoder 300 may beconfigured to insert the motion vectors of the last K HMVP candidates inthe table after the TMVP candidate. Video encoder 200 and/or videodecoder 300 may be configured to use only HMVP candidates with the samereference picture as the AMVP target reference picture to construct theAMVP candidate list. Video encoder 200 and/or video decoder 300 may beconfigured to apply pruning on the HMVP candidates.

Video encoder 200 and/or video decoder 300 may be configured to usepairwise average candidates in Chen, et al. “Algorithm description forVersatile Video Coding and Test Model 3 (VTM 3),” Joint Video ExpertsTeam (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 12 ^(th)Meeting: Macao, CN, 3-12 Oct. 2018, JVET-L1002-v1 (hereinafter“VTM3.0”). Video encoder 200 and/or video decoder 300 may be configuredto generate pairwise average candidates by averaging predefined pairs ofcandidates in the current merge candidate list (includes spatialcandidates, TMVP, and HMVP), and the predefined pairs are defined as{(0, 1), (0, 2), (1, 2), (0, 3), (1, 3), (2, 3)}, where the numbersdenote the merge indices to the merge candidate list. Video encoder 200and/or video decoder 300 may be configured to calculate the averagedmotion vectors separately for each reference list. If both motionvectors are available in one list, video encoder 200 and/or videodecoder 300 may be configured to average these two motion vectors evenwhen they point to different reference pictures; if only one motionvector is available, use the one directly; if no motion vector isavailable, keep this list invalid. The pairwise average candidatesreplace the combined candidates in HEVC standard.

FIG. 5A is a conceptual diagram illustrating example neighboring samples553A-553H of a current coding unit (CU) 551 used for derivingillumination compensation (IC) parameters. FIG. 5B is a conceptualdiagram illustrating example neighboring samples 557A-557H of areference block 555 used for deriving IC parameters. LIC is based on alinear model for illumination changes, using a scaling factor a and anoffset b. And LIC is enabled or disabled adaptively for each inter-modecoded coding unit (CU).

When LIC applies for a CU, video encoder 200 and/or video decoder 300may be configured to employ a least square error process to derive theparameters a and b by using neighbouring samples 553A-553H of thecurrent CU 551 and their corresponding reference samples. Morespecifically, as illustrated in FIG. 5A, video encoder 200 and/or videodecoder 300 may be configured to use the subsampled (2:1 subsampling)neighbouring samples 553A-553H of the CU 551. In the example of FIG. 5B,video encoder 200 and/or video decoder 300 may be configured to use thecorresponding pixels (identified by motion information of the current CUor sub-CU) in the reference picture. Video encoder 200 and/or videodecoder 300 may be configured to derive the IC parameters and apply theIC parameters for each prediction direction separately.

When a CU is coded with merge mode, video encoder 200 and/or videodecoder 300 may be configured to copy the LIC flag from neighbouringblocks, in a way similar to motion information copy in merge mode;otherwise, video encoder 200 may be configured to signal an LIC flag forthe CU to indicate whether LIC applies or not.

In HEVC, Weighted Prediction (WP) is supported, where a scaling factor(denoted by a), a shift number (denoted by s) and an offset (denoted byb) is used in the motion compensation. Suppose the pixel value inposition (x, y) of the reference picture is p(x, y), then video encoder200 and/or video decoder 300 may be configured to use p′(x, y)=((a*p(x,y)+(1<<(s−1)))>>s)+b instead of p(x, y) as the prediction value inmotion compensation.

When WP is enabled, for each reference picture of current slice, videoencoder 200 may be configured to signal a flag to indicate whether WPapplies for the reference picture or not. If WP applies for onereference picture, video encoder 200 may be configured to send a set ofWP parameters (i.e., a, s and b) to video decoder 300 and video decoder300 may use the set of WP parameters for motion compensation from thereference picture. To flexibly turn on/off WP for luma and chromacomponent, video encoder 200 may be configured to separately signal WPflag and WP parameters for luma and chroma components.

In WP, video encoder 200 and/or video decoder 300 may be configured touse one same set of WP parameters for all pixels in one referencepicture. Depending on the type of slice (P_SLICE or B_SLICE), videoencoder 200 and/or video decoder 300 may be configured to choose theweighting algorithm: (1) Default: the default HEVC uni-prediction orbi-prediction; (2) Explicit: the weighting factors are transmittedexplicitly in the slice header; (3) Implicit: the weighting factors forbi-prediction are derived from the distance of the current POC with thePOC of the reference pictures, relatively to the distance betweenreferences POC (B_SLICE only).

In the reference model of VVC, generalized bi-prediction (GBi) modeallows applying different weights to list 0 (L0) predictors and list 1(L1) predictors. The supported weight sets include one equal-weight setand four unequal-weight sets. Video encoder 200 may be configured toexplicitly signal the weight selection in GBi for one coding unit (CU)if this CU is coded by bi-prediction.

In an example bi-prediction, video encoder 200 and/or video decoder 300may be configured to average the predictors from L0 and L1 to generatethe final predictor using the equal weight 0.5. The predictor generationformula is shown as in Equation (1)

P _(TraditionalBiPred)=(P _(L0) +P _(L1)+RoundingOffset)>>shiftNum,  (1)

In Equation (1), P_(TraditionalBiPred) is the final predictor for thebi-prediction, P_(L0) and P_(L1) are predictors from L0 and L1,respectively, and RoundingOffset and shiftNum are used to normalize thefinal predictor. That is, P_(L0) is a first predictor for the firstreference picture and P_(L1) is a second predictor for the secondreference picture. In some examples, RoundingOffset is a predefinedoffset. In some examples, shiftNum is a predefined number of left shiftoperations.

In this disclosure, GBi is presented to allow applying different weightsto predictors from L0 and L1. The predictor generation is shown inEquation (2).

P _(GBi)((1−w ₁)*P _(L0) +w ₁ *P_(L1)+RoundingOffset_(GBi))>>shiftNum_(GBi),  (2)

In Equation (2), P_(GBi) is the final predictor of GBi. (1−w₁) and w₁are the selected GBi weights applied to the predictors of L0 and L1,respectively. RoundingOffset_(GBi) and shiftNum_(GBi) are used tonormalize the final predictor in GBi. In accordance with one or moretechniques described herein, a video coder (e.g., video encoder 200 orvideo decoder 300) may be configured to generate the predictioninformation by calculating equation 2.

In AMVP, if the inter prediction is bi-prediction, the GBi index issignaled based on truncated unary coding as shown in Table 1 and Table2.

TABLE 1 Binarization of GBi index GBi Weight value Binarization of GBiIndex of w₁ Index 0 −1/4  0000 1 3/8 001 2 1/2 1 3 5/8 01 4 5/4 0001

TABLE 2 Binarization of GBi index GBi Weight value Binarization of GBiIndex of w₁ Index 0 3/8 00 1 1/2 1 2 5/8 01

Weighted Prediction (WP) in HEVC has explicit mode in which weightingfactors for each reference frame are coded and transmitted. Forbi-directional prediction, video encoder 200 and/or video decoder 300may be configured to code two weighting factors. There may be no defaultmode for normalized weighted prediction. For example, if weightingfactor for the reference in list 0 is w₀, the weighting factor for thereference in the list 1 may be 1−w₀. In this case, video encoder 200and/or video decoder 300 may be configured to code only one weightingfactor. Video encoder 200 and/or video decoder 300 may be configured togenerate the other weighting factor by a default process.

In an example using normalized weighted prediction for bi-directionalprediction, video encoder 200 and/or video decoder 300 may be configuredto explicitly transmit one weighting factor of one reference andgenerate the weighting factor for the other reference by N minus thisone, where N can be 1, 2, 3, 4, 5 or other numbers. Said differently,for example, a video coder (e.g., video encoder 200 or video decoder300) may be configured to generate a first weighting factor for a firstreference picture in a first picture list using a second weightingfactor for a second reference picture in a second picture list. In someexamples, the video coder may be configured to calculate N minus thesecond weighting factor, where N is greater than zero and in someexamples an integer. In some instances, N is 1. For example, videodecoder 300 may be configured to decode N from a bitstream for videodata. Video encoder 200 may be configured to encode N in a bitstream forvideo data. In some examples, the value of N may be preset, and in suchexamples, video encoder 200 may not signal and video decoder 300 may notreceive the value of N from the bitstream.

In an example using reference indices, video encoder 200 and/or videodecoder 300 may be configured to indicate weighting factors for interblocks coded by weighted prediction through selection of one or morereference indices. For example, video encoder 200 and/or video decoder300 may be configured to code the weighting factor with the referenceindex of list 0 (or list 1 in the same way). In this example, “m” is thenumber of active references in each reference list and “n” is the numberof weighting factors. For instance, m=2 and n=5, there are m×n=2×5=10combinations. The binarization of reference index of list 0 (or list 1)with weighting factors is as below. The binarization of reference indexof list 1 (or list 0) may not change. For example, in the decoder side(e.g., video decoder 300), if the decoded value of reference index oflist 0 is 00001, the reference index of list 0 is 0, the associatedweighting factor of this reference frame in list 0 is ⅜, and theweighting factor of reference in list 1 is 1⅜=⅝.

TABLE 1 binarization of reference index of list 0 (or list 1) withweighting factors Reference Index of Weight value List 0 of wBinarization 0 1/2 1 1 1/2 01 0 5/8 001 1 5/8 0001 0 3/8 00001 1 3/8000001 0 5/4 0000001 1 5/4 00000001 0 −1/4  000000001 1 −1/4  000000000

Said differently, for example, a video coder (e.g., video encoder 200 orvideo decoder 300) may be configured to select a second referencepicture from a plurality of reference pictures of the second picturelist using a reference index and determine the second weighting factorusing the reference index. For instance, video decoder 300 may beconfigured to decode the reference index from a bitstream for videodata. Similarly, video encoder 200 may be configured to encode thereference index in a bitstream for video data.

In the example using normalized weighted prediction for bi-directionalprediction, video encoder 200 and/or video decoder 300 may be configuredto change the binarization of reference index with a weighting factoraccording to a selection probability. For example, video encoder 200and/or video decoder 300 may be configured to code a higher-probabilitycombination in fewer bits than a lower-probability combination.

In the example using normalized weighted prediction for bi-directionalprediction, video encoder 200 and/or video decoder 300 may be configuredto code the combination of reference index and weighting factor in otherprocesses such as the following truncated binary coding example.

TABLE 2 truncated binary coding example Reference Index of Weight valueList 0 of w Binarization 0 1/2 000 1 1/2 001 0 5/8 010 1 5/8 011 0 3/8100 1 3/8 101 0 5/4 1100 1 5/4 1101 0 −1/4  1110 1 −1/4  1111

Video encoder 200 and/or video decoder 300 may be configured to code theweighting factor with the reference index of list 0 and list 1. Videoencoder 200 and/or video decoder 300 may be configured to derive aweighting factor by decoding the reference indexes of list 0 and list 1.

In the example using reference indices, there are “m” weighting factorsand video encoder 200 and/or video decoder 300 may divide the mweighting factors into “x” bands. Each band includes a_(i) weightingfactors. Video encoder 200 and/or video decoder 300 may be configured tocode a band index with a reference index of list 1 (or List 0) and codea weighting factor in the band with a reference index of list 0 (or list1). For example, the number of active references in each list and thenumber of weighting factors may be the same as the example of Table 1.Video encoder 200 and/or video decoder 300 may be configured to dividethe set of weighing factors into 3 bands, where band 0 includes {½},band 1 includes {⅝, ⅜}, and band 2 includes {5/4, −¼} as shown in Table3.

TABLE 3 An example set of weighing factors divided into 3 bandsReference Reference Reference Reference Weighting index of of List 1index of of List 0 Band factor list 1 Binarization list 0 BinarizationBand 0 1/2 0 1 0 1 1 01 1 01 0 1 1 01 Band 1 5/8 0 001 0 1 1 01 1 0001 01 1 01 3/8 0 001 0 001 1 000 1 0001 0 001 1 000 Band 2 5/4 0 00001 0 1 101 1 00000 0 1 1 01 −1/4  0 00001 0 001 1 000 1 00000 0 001 1 000

Said differently, for example, a video coder (e.g., video encoder 200 orvideo decoder 300) may be configured to determine a second weightingfactor using a band of a plurality of bands, each band of the pluralityof bands including a plurality of weight factors.

In the example using reference indices, video encoder 200 and/or videodecoder 300 may be configured to change the binarization of referenceindex with weighting factor according to selection probability. Ahigher-probability combination may be coded in fewer bits.

In the example using reference indices, video encoder 200 and/or videodecoder 300 may be configured to code the combinations of referenceindex and weighting factor in other processes such as truncated binaryencoding.

Normalization mode flag, the weighting factors, and the sum N (forexample, N equal to 1) of two weighting factors of a bi-prediction blockcan be pre-defined in both encoder side (e.g., video encoder 200) anddecoder side (e.g., video decoder 300), or be set as a set of valuessignaled from the encoder to the decoder at sequence level, picturelevel, slice level, tile level or block level. For example, videoencoder 200 may be configured to signal one or more of a normalizationmode flag, one or more weighting factors, or a sum N (for example, Nequal to 1) of two weighting factors of a bi-prediction block in aSequence Parameter Set (SPS), Picture Parameter Set (PPS), Slice header(SH), Tile, Coding Tree Unit (CTU) or Coding Unit (CU).

In some examples, video encoder 200 and/or video decoder 300 may beconfigured to use a weighted prediction coding process, where theweighting factors can be any values.

Video encoder 200 and/or video decoder 300 may be configured to imposean extra constraint on weighted bi-prediction. For example, videoencoder 200 may be configured to signal a picture-level flag, referredto as constrained_wbi_indicator, when the picture-level flag, referredto as weighted_bipred_flag, is set equal to 1 and the slice type isB-Slice. Video encoder 200 and/or video decoder 300 may be configured touse these indicators to specify the number of weighting factors inaddition to ½. When constrained_wbi_flag is set equal 0, video decoder300 may be configured to perform the weighted bi-prediction as-iswithout change. Otherwise, when constrained_wbi_flag is set equal to n(where n=1, 2, 3, . . . ), video decoder 300 may be configured toperform the constrained weighted bi-prediction performs as follows inthe description of the extension of reference index process, thedescription of constrained weighted factor assignment, and thedescription of the mapping function from the L1 reference index to thereference picture.

In an example extension of reference index process, video encoder 200and/or video decoder 300 may be configured to allow the slice-levelindicator (num_ref_idx_l1_active_minus1) to go beyond its maximal value(i.e. 14). For example, there are 15 reference pictures in List 1 atmaximum. In this way, video encoder 200 and/or video decoder 300 may beconfigured to code extra reference indices beyond 14 reference picturesas a suffix appended to the truncated unary code ofnum_ref_idx_l0_active_minus1 and num_ref_idx_l1_active_minus1.Specifically, for example, this suffix is represented by using truncatedbinary code.

In an example constrained weighted factor assignment, video encoder 200and/or video decoder 300 may be configured to couple only weightingfactors with the reference pictures in List 1, while the respectiveweighting factors of reference pictures in List 0 are determineddepending on whichever reference picture in List 1 is selected. Forexample, if the weighting factor of a L1 reference picture is w, videoencoder 200 and/or video decoder 300 may be configured to determine theweighting factor of each L0 reference picture is N−w, where N followsthe same rule as proposed in the normalized weighted prediction processdescribed herein.

In an example mapping function from L1 reference index to referencepicture and weighting factor, video encoder 200 and/or video decoder 300may be configured to apply a mapping function from a reference index toa reference picture and weighting factors as follows. Supposing thereare m reference pictures {p₁(0), p₁(1), . . . , p₁(m−1)} in List 1 and nweighting factors {w₀, w₁, . . . , w_(n-1)}, video encoder 200 and/orvideo decoder 300 may be configured to map the first m reference indices(e.g., m reference pictures with the weighting factor of w₀) followingthe same ordered sequence as {p₁(0), p₁(1), . . . , p₁(m−1)} with w₀,and map the second m reference indices (e.g., m reference pictures withthe weighting factor of w₁) in the above same way but the associatedweighting factor is w₁, and so on. Specifically, this mapping functionfrom a received L1 reference (r₁) to reference picture (p₁(i)) andweighting factor (w_(j)) can be formulated as follows:

i=r ₁% n,

j=floor(r ₁ /n).

In this disclosure, for example, the actual number of reference picturesin List 1 may be equal to m by n. Table 4 below gives an example withm=3 and n=3.

TABLE 4 reference pictures in List 1 RefIdx 0 1 2 3 4 5 6 7 8 L1 RefPicp₁(0) p₁(1) p₁(2) p₁(0) p₁(1) p₁(2) p₁(0) p₁(1) p₁(2) L1 Weight w₀ w₀ w₀w₁ w₁ w₁ w₂ w₂ w₂ L1

Supposing there are 4 reference pictures {p₀(0), p₀(1), p₀(2), p₀(3)} inList 0 and the received reference index is 6 from Table 4, then Table 5below gives an example of weighting factor assignment for L0.

TABLE 5 examples of weighting factor assignment for L0 RefIdx L0 0 1 2 3RefPic L0 p₀(0) p₀(1) p₀(2) p₀(0) Weight L0 N − w₂ N − w₂ N − w₂ N − w₂

Video encoder 200 and/or video decoder 300 may be configured to assignthe ½ weighting factor to either w₀ or w₁ for signalling efficiency.

In the foregoing examples, all L0 and L1 in the above description can beswapped. Said differently, for example, the first picture list may belist 0 (L0) and the second picture list may be list 1 (L1) or the firstpicture list may be list 1 (L1) and the second picture list may be list0 (L0).

FIG. 6 is a block diagram illustrating an example video encoder 200 thatmay perform the techniques of this disclosure. FIG. 6 is provided forpurposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 200 inthe context of video coding standards such as the HEVC video codingstandard and the H.266 video coding standard in development. However,the techniques of this disclosure are not limited to these video codingstandards, and are applicable generally to video encoding and decoding.

In the example of FIG. 6, video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220. Any or all of video data memory 230, mode selection unit 202,residual generation unit 204, transform processing unit 206,quantization unit 208, inverse quantization unit 210, inverse transformprocessing unit 212, reconstruction unit 214, filter unit 216, DPB 218,and entropy encoding unit 220 may be implemented in one or moreprocessors or in processing circuitry. Moreover, video encoder 200 mayinclude additional or alternative processors or processing circuitry toperform these and other functions.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 1). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random-access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 1 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 6 are illustrated to assist with understandingthe operations performed by video encoder 200. The units may beimplemented as fixed-function circuits, programmable circuits, or acombination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality, and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that canprogrammed to perform various tasks, and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, the one or more of the units maybe distinct circuit blocks (fixed-function or programmable), and in someexamples, the one or more units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 1) may store theobject code of the software that video encoder 200 receives andexecutes, or another memory within video encoder 200 (not shown) maystore such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, weightpredictor unit 223, motion compensation unit 224, and anintra-prediction unit 226. Mode selection unit 202 may includeadditional functional units to perform video prediction in accordancewith other prediction modes. As examples, mode selection unit 202 mayinclude a palette unit, an intra-block copy unit (which may be part ofmotion estimation unit 222 and/or motion compensation unit 224), anaffine unit, a linear model (LM) unit, or the like.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 202 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that defines the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate, with weight predictor unit 223, a prediction blockusing the motion vectors. For example, motion compensation unit 224 mayretrieve data of the reference block using the motion vector. As anotherexample, if the motion vector has fractional sample precision, motioncompensation unit 224 may interpolate values for the prediction blockaccording to one or more interpolation filters. Moreover, forbi-directional inter-prediction, motion compensation unit 224 mayretrieve data for two reference blocks identified by respective motionvectors and combine, weight predictor unit 223, the retrieved data,e.g., through sample-by-sample averaging or weighted averaging.

Motion selection unit 202 and, more specifically, weight predictor unit223 may be configured to generate a first weighting factor for a firstreference picture in a first picture list using a second weightingfactor for a second reference picture in a second picture list.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

Mode selection unit 202 provides the prediction block to residualgeneration unit 204. Residual generation unit 204 receives a raw,uncoded version of the current block from video data memory 230 and theprediction block from mode selection unit 202. Residual generation unit204 calculates sample-by-sample differences between the current blockand the prediction block. The resulting sample-by-sample differencesdefine a residual block for the current block. In some examples,residual generation unit 204 may also determine differences betweensample values in the residual block to generate a residual block usingresidual differential pulse code modulation (RDPCM). In some examples,residual generation unit 204 may be formed using one or more subtractorcircuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma prediction unit and correspondingchroma prediction units. Video encoder 200 and video decoder 300 maysupport PUs having various sizes. As indicated above, the size of a CUmay refer to the size of the luma coding block of the CU and the size ofa PU may refer to the size of a luma prediction unit of the PU. Assumingthat the size of a particular CU is 2N×2N, video encoder 200 may supportPU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder20 and video decoder 30 may also support asymmetric partitioning for PUsizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

In examples where mode selection unit does not further partition a CUinto PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 120 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as an intra-block copy modecoding, an affine-mode coding, and linear model (LM) mode coding, as fewexamples, mode selection unit 202, via respective units associated withthe coding techniques, generates a prediction block for the currentblock being encoded. In some examples, such as palette mode coding, modeselection unit 202 may not generate a prediction block, and insteadgenerate syntax elements that indicate the manner in which toreconstruct the block based on a selected palette. In such modes, modeselection unit 202 may provide these syntax elements to entropy encodingunit 220 to be encoded.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block.

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a directional transform, aKarhunen-Loeve transform (KLT), or a conceptually similar transform to aresidual block. In some examples, transform processing unit 206 mayperform multiple transforms to a residual block, e.g., a primarytransform and a secondary transform, such as a rotational transform. Insome examples, transform processing unit 206 does not apply transformsto a residual block.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value associated with the current block.Video encoder 200 (e.g., via mode selection unit 202) may adjust thedegree of quantization applied to the coefficient blocks associated withthe current block by adjusting the QP value associated with the CU.Quantization may introduce loss of information, and thus, quantizedtransform coefficients may have lower precision than the originaltransform coefficients produced by transform processing unit 206.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. Reconstruction unit 214 mayproduce a reconstructed block corresponding to the current block (albeitpotentially with some degree of distortion) based on the reconstructedresidual block and a prediction block generated by mode selection unit202. For example, reconstruction unit 214 may add samples of thereconstructed residual block to corresponding samples from theprediction block generated by mode selection unit 202 to produce thereconstructed block.

Filter unit 216 may perform one or more filter operations onreconstructed blocks. For example, filter unit 216 may performdeblocking operations to reduce blockiness artifacts along edges of CUs.Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance,in examples where operations of filter unit 216 are not needed,reconstruction unit 214 may store reconstructed blocks to DPB 218. Inexamples where operations of filter unit 216 are needed, filter unit 216may store the filtered reconstructed blocks to DPB 218. Motionestimation unit 222 and motion compensation unit 224 may retrieve areference picture from DPB 218, formed from the reconstructed (andpotentially filtered) blocks, to inter-predict blocks of subsequentlyencoded pictures. In addition, intra-prediction unit 226 may usereconstructed blocks in DPB 218 of a current picture to intra-predictother blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream.

The operations described above are described with respect to a block.Such description should be understood as being operations for a lumacoding block and/or chroma coding blocks. As described above, in someexamples, the luma coding block and chroma coding blocks are luma andchroma components of a CU. In some examples, the luma coding block andthe chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying a MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding blocks andthe chroma coding blocks.

Video encoder 200 represents an example of a device configured to encodevideo data including a memory configured to store video data, and one ormore processing units implemented in circuitry and configured togenerate a first weighting factor for a first reference picture in afirst picture list using a second weighting factor for a secondreference picture in a second picture list and generate predictioninformation for a current block of the video data using the firstweighting factor and the second weighting factor.

FIG. 7 is a block diagram illustrating an example video decoder 300 thatmay perform the techniques of this disclosure. FIG. 7 is provided forpurposes of explanation and is not limiting on the techniques as broadlyexemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 is describedaccording to the techniques of JEM and HEVC. However, the techniques ofthis disclosure may be performed by video coding devices that areconfigured to other video coding standards.

In the example of FIG. 7, video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropydecoding unit 302, prediction processing unit 304, inverse quantizationunit 306, inverse transform processing unit 308, reconstruction unit310, filter unit 312, and DPB 314 may be implemented in one or moreprocessors or in processing circuitry. Moreover, video decoder 300 mayinclude additional or alternative processors or processing circuitry toperform these and other functions.

Prediction processing unit 304 includes motion compensation unit 316 andintra-prediction unit 318. Prediction processing unit 304 may includeaddition units to perform prediction in accordance with other predictionmodes. As examples, prediction processing unit 304 may include a paletteunit, an intra-block copy unit (which may form part of motioncompensation unit 318), an affine unit, a linear model (LM) unit, or thelike. In other examples, video decoder 300 may include more, fewer, ordifferent functional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 1). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements) from an encodedvideo bitstream. Also, CPB memory 320 may store video data other thansyntax elements of a coded picture, such as temporary data representingoutputs from the various units of video decoder 300. DPB 314 generallystores decoded pictures, which video decoder 300 may output and/or useas reference video data when decoding subsequent data or pictures of theencoded video bitstream. CPB memory 320 and DPB 314 may be formed by anyof a variety of memory devices, such as dynamic random-access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. CPB memory 320and DPB 314 may be provided by the same memory device or separate memorydevices. In various examples, CPB memory 320 may be on-chip with othercomponents of video decoder 300, or off-chip relative to thosecomponents.

Additionally, or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 1). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to executed by processing circuitry of video decoder 300.

The various units shown in FIG. 7 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 6, fixed-function circuits referto circuits that provide particular functionality, and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can programmed to perform various tasks, and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, the one ormore of the units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, the one or more units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a quantizationparameter (QP) and/or transform mode indication(s). Inverse quantizationunit 306 may use the QP associated with the quantized transformcoefficient block to determine a degree of quantization and, likewise, adegree of inverse quantization for inverse quantization unit 306 toapply. Inverse quantization unit 306 may, for example, perform a bitwiseleft-shift operation to inverse quantize the quantized transformcoefficients. Inverse quantization unit 306 may thereby form a transformcoefficient block including transform coefficients.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT, an inverseinteger transform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the coefficient block.

Furthermore, prediction processing unit 304 generates a prediction blockaccording to prediction information syntax elements that were entropydecoded by entropy decoding unit 302. For example, if the predictioninformation syntax elements indicate that the current block isinter-predicted, motion compensation unit 316 may generate, with weightpredictor unit 317, the prediction block. In this case, the predictioninformation syntax elements may indicate a reference picture in DPB 314from which to retrieve a reference block, as well as a motion vectoridentifying a location of the reference block in the reference picturerelative to the location of the current block in the current picture.Motion compensation unit 316 may generally perform the inter-predictionprocess in a manner that is substantially similar to that described withrespect to motion compensation unit 224 (FIG. 6). For example,prediction processing unit 304 and, more specifically, weight predictorunit 317 may be configured to generate a first weighting factor for afirst reference picture in a first picture list using a second weightingfactor for a second reference picture in a second picture list.

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 6).Intra-prediction unit 318 may retrieve data of neighboring samples tothe current block from DPB 314.

Reconstruction unit 310 may reconstruct the current block using theprediction block and the residual block. For example, reconstructionunit 310 may add samples of the residual block to corresponding samplesof the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations onreconstructed blocks. For example, filter unit 312 may performdeblocking operations to reduce blockiness artifacts along edges of thereconstructed blocks. Operations of filter unit 312 are not necessarilyperformed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. Asdiscussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures fromDPB for subsequent presentation on a display device, such as displaydevice 118 of FIG. 1.

In this manner, video decoder 300 represents an example of a videodecoding device including a memory configured to store video data, andone or more processing units implemented in circuitry and configured togenerate a first weighting factor for a first reference picture in afirst picture list using a second weighting factor for a secondreference picture in a second picture list and generate predictioninformation for a current block of the video data using the firstweighting factor and the second weighting factor.

FIG. 8 is a flowchart illustrating an example method for encoding acurrent block. The current block may comprise a current CU. Althoughdescribed with respect to video encoder 200 (FIGS. 1 and 2), it shouldbe understood that other devices may be configured to perform a methodsimilar to that of FIG. 8.

In this example, video encoder 200 initially predicts the current block(350). For example, video encoder 200 may form a prediction block forthe current block. In some examples, video encoder 200 may generate afirst weighting factor for a first reference picture in a first picturelist using a second weighting factor for a second reference picture in asecond picture list and generate prediction information using the firstweighting factor and the second weighting factor.

Video encoder 200 may then calculate a residual block for the currentblock (352). For example, video encoder 200 may generate a residualblock for the current block using the current block and the predictioninformation and encode the residual block as follows. To calculate theresidual block, video encoder 200 may calculate a difference between theoriginal, uncoded block and the prediction block for the current block.Video encoder 200 may then transform and quantize coefficients of theresidual block (354). Next, video encoder 200 may scan the quantizedtransform coefficients of the residual block (356). During the scan, orfollowing the scan, video encoder 200 may entropy encode thecoefficients (358). For example, video encoder 200 may encode thecoefficients using CAVLC or CABAC. Video encoder 200 may then output theentropy coded data of the block (360).

FIG. 9 is a flowchart illustrating an example method for decoding acurrent block of video data. The current block may comprise a currentCU. Although described with respect to video decoder 300 (FIGS. 1 and3), it should be understood that other devices may be configured toperform a method similar to that of FIG. 9.

Video decoder 300 may receive entropy coded data for the current block,such as entropy coded prediction information and entropy coded data forcoefficients of a residual block corresponding to the current block(370). Video decoder 300 may entropy decode the entropy coded data todetermine prediction information for the current block and to reproducecoefficients of the residual block (372). Video decoder 300 may predictthe current block (374), e.g., using an intra- or inter-prediction modeas indicated by the prediction information for the current block, tocalculate a prediction block for the current block. In some examples,video decoder 300 may generate a first weighting factor for a firstreference picture in a first picture list using a second weightingfactor for a second reference picture in a second picture list andgenerate prediction information using the first weighting factor and thesecond weighting factor. In this example, video decoder 300 may predictthe current block using the prediction information. For instance, videodecoder 300 may predict the current block by applying equation 2 withthe first weighting factor and the second weighting factor.

Video decoder 300 may then inverse scan the reproduced coefficients(376), to create a block of quantized transform coefficients. Videodecoder 300 may then inverse quantize and inverse transform thecoefficients to produce a residual block (378). Video decoder 300 mayultimately decode the current block by combining the prediction blockand the residual block (380). For example, video decoder 300 may decodea residual block for the current block and decode the current blockusing the prediction information and the residual block.

FIG. 10 is a flowchart illustrating an example process for weightprediction. The current block may comprise a current CU. Althoughdescribed with respect to video encoder 200 (FIGS. 1 and 2), it shouldbe understood that other devices may be configured to perform a methodsimilar to that of FIG. 10.

In this example, a video coder (e.g., video encoder 200 or video decoder300) may be configured to generate a first weighting factor for a firstreference picture in a first picture list using a second weightingfactor for a second reference picture in a second picture list (382).For example, weight predictor unit 223 of video encoder 200 may beconfigured to generate a first weighting factor for a first referencepicture in a first picture list using a second weighting factor for asecond reference picture in a second picture list. in some examples,weight predictor unit 317 of video decoder 300 may be configured togenerate a first weighting factor for a first reference picture in afirst picture list using a second weighting factor for a secondreference picture in a second picture list.

The video coder may be configured to generate prediction information fora current block of the video data using the first weighting factor andthe second weighting factor (384). For example, the video coder maycalculate equation 2 using the first weighting factor and the secondweighting factor. The video coder may be configured to predict thecurrent block using the prediction information (386). For example, modeselection unit 202 of video encoder 200 may predict the current blockusing the prediction information. In some examples, predictionprocessing unit 304 of video decoder 300 may predict the current blockusing the prediction information.

Illustrative examples of the disclosure include:

Example 1: A method of processing video data, the method comprising:generating a first weighting factor for a first reference picture in afirst picture list using a second weighting factor for a secondreference picture in a second picture list; and generating predictioninformation using the first weighting factor and the second weightingfactor.

Example 2: The method of example 1, wherein generating the firstweighting factor comprises: calculating N minus the second weightingfactor, wherein N is an integer.

Example 3: The method of example 2, wherein N is signaled.

Example 4: The method of any one of examples 1-3, further comprising:determining the second weighting factor using a selection of referenceindices, wherein generating the first weighting factor comprisesgenerating the first weighting factor based on the determined secondweighting factor.

Example 5: The method of any one of examples 1-4, further comprising:determining the second weighting factor using a band.

Example 6: The method of any of examples 1-5, wherein the first picturelist is list 0 (L0) and the second picture list is list 1 (L1); orwherein the first picture list is list 1 (L1) and the second picturelist is list 0 (L0).

Example 7: The method of any of examples 1-6, further comprising:decoding a current block based on the prediction information.

Example 8: The method of any of examples 1-6, further comprising:encoding a current block based on the prediction information.

Example 9: A device for coding video data, the device comprising one ormore means for performing the method of any of examples 1-6.

Example 10: The device of example 9, wherein the one or more meanscomprise one or more processors implemented in circuitry.

Example 11: The device of any of examples 9 and 10, further comprising amemory to store the video data.

Example 12: The device of any of examples 9-11, further comprising adisplay configured to display decoded video data.

Example 13: The device of any of examples 9-12, wherein the devicecomprises one or more of a camera, a computer, a mobile device, abroadcast receiver device, or a set-top box.

Example 14: The device of any of examples 9-13, wherein the devicecomprises a video decoder.

Example 15: The device of any of examples 9-14, wherein the devicecomprises a video encoder.

Example 16: A computer-readable storage medium having stored thereoninstructions that, when executed, cause one or more processors toperform the method of any of examples 1-6.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the terms “processor” and “processingcircuitry,” as used herein may refer to any of the foregoing structuresor any other structure suitable for implementation of the techniquesdescribed herein. In addition, in some aspects, the functionalitydescribed herein may be provided within dedicated hardware and/orsoftware modules configured for encoding and decoding, or incorporatedin a combined codec. Also, the techniques could be fully implemented inone or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of processing video data, the methodcomprising: generating, by one or more processors implemented incircuitry, a first weighting factor for a first reference picture in afirst picture list using a second weighting factor for a secondreference picture in a second picture list; and generating, by the oneor more processors, prediction information for a current block of thevideo data using the first weighting factor and the second weightingfactor.
 2. The method of claim 1, wherein generating the first weightingfactor comprises: calculating N minus the second weighting factor. 3.The method of claim 2, wherein N is
 1. 4. The method of claim 2, furthercomprising: decoding, by the one or more processors, N from a bitstreamfor the video data.
 5. The method of claim 2, further comprising:encoding, by the one or more processors, N in a bitstream for the videodata.
 6. The method of claim 1, further comprising: selecting, by theone or more processors, the second reference picture from a plurality ofreference pictures of the second picture list using a reference index;and determining, by the one or more processors, the second weightingfactor using the reference index.
 7. The method of claim 6, furthercomprising: decoding, by the one or more processors, the reference indexfrom a bitstream for the video data.
 8. The method of claim 6, furthercomprising: encoding, by the one or more processors, the reference indexin a bitstream for the video data.
 9. The method of claim 1, furthercomprising: determining, by the one or more processors, the secondweighting factor using a band of a plurality of bands, each band of theplurality of bands including a plurality of weight factors.
 10. Themethod of claim 1, wherein generating the prediction informationcomprises calculating:P _(GBi)((1−w ₁)*P _(L0) +w ₁ *P_(L1)+RoundingOffset_(GBi))>>shiftNum_(GBi), wherein P_(GBi) is theprediction information, P_(L0) is a first predictor for the firstreference picture, P_(L1) is a second predictor for the second referencepicture, RoundingOffset is a predefined offset, shiftNum is a predefinednumber of left shift operations, w₁ is the second weighting factor, and(1−w₁) is the first weighting factor.
 11. The method of claim 1, whereinthe first picture list is list 0 (L0) and the second picture list islist 1 (L1), or wherein the first picture list is list 1 (L1) and thesecond picture list is list 0 (L0).
 12. The method of claim 1,comprising: decoding, by the one or more processors, a residual blockfor the current block; and decoding, by the one or more processors, thecurrent block using the prediction information and the residual block.13. The method of claim 1, comprising: generating, by the one or moreprocessors, a residual block for the current block using the currentblock and the prediction information; and encoding, by the one or moreprocessors, the residual block.
 14. A device for processing video data,the device comprising: a memory configured to store video data; and oneor more processors implemented in circuitry and configured to: generatea first weighting factor for a first reference picture in a firstpicture list using a second weighting factor for a second referencepicture in a second picture list; and generate prediction informationfor a current block of the video data using the first weighting factorand the second weighting factor.
 15. The device of claim 14, wherein, togenerate the first weighting factor, the one or more processors areconfigured to: calculate N minus the second weighting factor.
 16. Thedevice of claim 15, wherein N is
 1. 17. The device of claim 15, whereinthe one or more processors are configured to: decode N from a bitstreamfor the video data.
 18. The device of claim 15, wherein the one or moreprocessors are configured to: encode N from a bitstream for the videodata.
 19. The device of claim 14, wherein the one or more processors areconfigured to: select the second reference picture from a plurality ofreference pictures of the second picture list using a reference index;and determine the second weighting factor using the reference index. 20.The device of claim 19, further comprising: decode the reference indexfrom a bitstream for the video data.
 21. The device of claim 20, furthercomprising: encode the reference index in a bitstream for the videodata.
 22. The device of claim 14, wherein the one or more processors areconfigured to: determine the second weighting factor using a band of aplurality of bands, each band of the plurality of bands including aplurality of weight factors.
 23. The device of claim 14, wherein, togenerate the prediction information, the one or more processors areconfigured to calculate:P _(GBi)((1−w ₁)*P _(L0) +w ₁ *P_(L1)+RoundingOffset_(GBi))>>shiftNum_(GBi), wherein P_(GBi) is theprediction information, P_(L0) is a first predictor for the firstreference picture, P_(L1) is a second predictor for the second referencepicture, RoundingOffset is a predefined offset, shiftNum is a predefinednumber of left shift operations, w₁ is the second weighting factor, and(1−w₁) is the first weighting factor.
 24. The device of claim 14,wherein the first picture list is list 0 (L0) and the second picturelist is list 1 (L1); or wherein the first picture list is list 1 (L1)and the second picture list is list 0 (L0).
 25. The device of claim 14,wherein the one or more processors are configured to: decode a residualblock for the current block; and decode the current block using theprediction information and the residual block.
 26. The device of claim14, wherein the one or more processors are configured to: generate aresidual block for the current block using the current block and theprediction information; and encode the residual block.
 27. The device ofclaim 14, wherein the device comprises one or more of a camera, acomputer, a mobile device, a broadcast receiver device, or a set-topbox.
 28. A computer-readable storage medium having stored thereoninstructions that, when executed, cause a processor to: generate a firstweighting factor for a first reference picture in a first picture listusing a second weighting factor for a second reference picture in asecond picture list; and generate prediction information for a currentblock of the video data using the first weighting factor and the secondweighting factor.
 29. A device for coding video data, the devicecomprising: means for generating a first weighting factor for a firstreference picture in a first picture list using a second weightingfactor for a second reference picture in a second picture list; andmeans for generating prediction information for a current block of thevideo data using the first weighting factor and the second weightingfactor.